It may be due to this breaking change in Eclipse 3.6:
http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.platform.doc.isv/porting/3.6/incompatibilities.html?view=co#objectContribution
EDIT:
Looks like it definitely is. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=309074. Here’s the fix:
In the “Customize Perspective” dialog, go to the “Command Groups Availability” tab and check “Team” and “SVN”.
In Eclipse Mars.2 (4.5.2) this is under Window->Perspective->Customize Perspective… dialog, “Action Set Availability” tab. (Try to restart Eclipse if it doesn’t work after you change it).
Customize Perspective dialog screenshot